<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
		<script type="text/javascript">
			//1.定义a   2.a=10  3.alert(a)
			var a = 10;
			alert(a)
			
			alert(b);
			var b;
			
			b();
			
			function b(){
				alert(1)
			}
		</script>
	</body>
</html>
